POS0742 CLUSTERS OF JUVENILE PSORIATIC ARTHRITIS IDENTIFIED AT INITIAL PRESENTATION TO PAEDIATRIC RHEUMATOLOGY IN A NATIONWIDE UK COHORT
Authors: S. Shoop-Worrall, C. Ciurtin, G. Cleary, F. Mcerlane, L. Coates, N. Geifman, K. Hyrich
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> The heterogenous presentation and variable clinical response of juvenile psoriatic arthritis (JPsA) to disease-modifying therapies suggests undiscovered subgroups within this disease. Nevertheless, JPsA is often studied under the umbrella of juvenile idiopathic arthritis (JIA), with few studies interrogating JPsA separately. To improve stratified treatment of this rare disease, such subgroups must be uncovered. <h3>Objectives</h3> To identify novel, phenotypically consistent subgroups of children and young people (CYP) with JPsA at the point of first contact with paediatric rheumatology. <h3>Methods</h3> CYP were initially selected if enrolled between January 2001 and December 2019 to the Childhood Arthritis Prospective Study, a UK, multicentre, prospective inception cohort of JIA. Those who had a physician's diagnosis of JPsA at any time point through the 10-year follow-up were included, to allow for onset of psoriatic signs after initial diagnosis. At initial presentation to paediatric rheumatology, clinical features within the ILAR classification criteria for JPsA were collected: an active joint count and the presence or absence of psoriasis, dactylitis and nail abnormalities. Latent class analysis used these features to identify clusters of disease. Between one and ten clusters were tested and an optimal model selected based on statistical fit. <h3>Results</h3> Of 1,753 CYP with JIA recruited to CAPS within the study period, a total of 161 CYP had ever had a diagnosis of JPsA (n=97 diagnosed as JPsA at initial presentation to paediatric rheumatology). The majority were female (61%), of white ethnicity (94%) and the median age at initial presentation was 10 years (IQR 6, 13). The optimal latent class model identified two clusters of JPsA. An oligoarticular cluster (90%, median active joint count (IQR): 2 (1,5)) had a higher proportion of CYP affected by psoriasis (Cluster 1: 29%, Cluster 2: 14%). A polyarticular cluster (10%, median active joint count (IQR): 20 (16, 27)) had a higher proportion with nail abnormalities (Cluster 1: 8%, Cluster 2: 27%). There were similar proportions of dactylitis among the clusters (Cluster 1: 18%, Cluster 2: 15%) (Figure 1). <h3>Conclusion</h3> This study identifies two clusters of JPsA at initial presentation to paediatric rheumatology with differences in key features used to classify this disease. Such subgroups may have different experiences of disease, and future analysis will explore characteristics, alongside disease impact and response to therapy for these groups. <h3>Acknowledgements</h3> We thank all the children and young people and their families involved in CAPS as well as clinical staff and administrators. We also thank the data management team at the University of Manchester (UK). This work is funded by the Medical Research Council (MR/W027151/1), and is also supported by Versus Arthritis (UK grant numbers 20542 &amp; 21755) and the NIHR Manchester Biomedical Research Centre (NIHR203308). <h3>Disclosure of Interests</h3> Stephanie Shoop-Worrall: None declared, Coziana Ciurtin: None declared, Gavin Cleary: None declared, Flora McErlane: None declared, Laura Coates: None declared, Nophar Geifman: None declared, Kimme Hyrich Speakers bureau: AbbVie, Grant/research support from: BMS and Pfizer.